Indian Ocean circulation and productivity during the last glacial cycle

Piotrowski, Alexander M; Banakar, V.K.; Scrivner, A. E.; Elderfield, Henry; Galy, Αlbert; Dennis, Aileen

doi:10.1016/j.epsl.2009.06.007

Cited by 106 publications

(98 citation statements)

References 77 publications

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“…3C) (28,29). In the case of the southern Atlantic record, synchronous δ 13 C variations have been found, indicating the possibility of circulation-driven changes in the carbon content of deep waters during these variations (29).…”

Section: Discussionmentioning

confidence: 85%

Mode change of millennial CO ₂ variability during the last glacial cycle associated with a bipolar marine carbon seesaw

Bereiter

Lüthi

Siegrist

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

156

188

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Important elements of natural climate variations during the last ice age are abrupt temperature increases over Greenland and related warming and cooling periods over Antarctica. Records from Antarctic ice cores have shown that the global carbon cycle also plays a role in these changes. The available data shows that atmospheric CO 2 follows closely temperatures reconstructed from Antarctic ice cores during these variations. Here, we present new high-resolution CO 2 data from Antarctic ice cores, which cover the period between 115,000 and 38,000 y before present. Our measurements show that also smaller Antarctic warming events have an imprint in CO 2 concentrations. Moreover, they indicate that during Marine Isotope Stage (MIS) 5, the peak of millennial CO 2 variations lags the onset of Dansgaard/Oeschger warmings by 250 AE 190 y. During MIS 3, this lag increases significantly to 870 AE 90 y. Considerations of the ocean circulation suggest that the millennial variability associated with the Atlantic Meridional Overturning Circulation (AMOC) undergoes a mode change from MIS 5 to MIS 4 and 3. Ocean carbon inventory estimates imply that during MIS 3 additional carbon is derived from an extended mass of carbon-enriched Antarctic Bottom Water. The absence of such a carbon-enriched water mass in the North Atlantic during MIS 5 can explain the smaller amount of carbon released to the atmosphere after the Antarctic temperature maximum and, hence, the shorter lag. Our new data provides further constraints for transient coupled carbon cycleclimate simulations during the entire last glacial cycle.abrupt climate change | CO2-temperature phasing | ice age variability | paleoclimate | greenhouse gas T he climate of the last glacial period is characterized by low global mean temperatures and a number of interhemispheric variations on time scales of several millennia. In the northern hemisphere, in particular on the Greenland ice sheet, large and very rapid temperature jumps of up to 15°C within a few decades, followed by more steady decreases of temperature, have been identified from ice core analyses (1, 2). 25 of these so-called Dansgaard-Oeschger (DO) events have been found during the last glacial period. For each of these events, an associated Antarctic temperature variation has been also documented in Antarctic ice cores (Antarctic Isotope Maximum [AIM] events) (3). Antarctic temperatures increase siteadily when Greenland is in the cold phase and slowly decrease following the abrupt temperature increase in Greenland during a DO event. This behavior is explained by the concept of an oceanic thermal bipolar seesaw, where variations in the Atlantic Meridional Overturning Circulation (AMOC) and associated changes in heat transport across the equator to the North Atlantic modulate the southern and northern hemisphere temperatures during each of these events (4).Previous reconstructions of atmospheric CO 2 concentrations during these millennial-scale variations show that CO 2 varies largely in parallel with the major AIM events (...

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Section: Discussionmentioning

confidence: 85%

Mode change of millennial CO ₂ variability during the last glacial cycle associated with a bipolar marine carbon seesaw

Bereiter

Lüthi

Siegrist

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

156

188

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“…Anyway, our results indicate that changes of considerable magnitude and spatial extent are required to affect Nd in seawater in a manner comparable e.g., to the magnitude of variations of about 3 Nd -unit that have been reconstructed from sediment records from the Cape Basin in the southeast Atlantic Ocean [Rutberg et al, 2000;Piotrowski et al, 2008] and the Indian Ocean [Piotrowski et al, 2009]. Nevertheless, due to the fact that the boundary source is applied at the sediment surface between the sea surface and 3000 m depth, effects on Nd emerge throughout the water column.…”

Section: Changes In the Nd Boundary Sourcementioning

confidence: 96%

Sensitivity of Nd isotopic composition in seawater to changes in Nd sources and paleoceanographic implications

Rempfer¹,

Stocker²,

Joos³

et al. 2012

J. Geophys. Res.

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.[1] It has been argued that past changes in the sources of Nd could hamper the use of the Nd isotopic composition ( Nd ) as a proxy for past changes in the overturning of deep water masses. Here we reconsider uncertainties associated with Nd in seawater due to potential regional to global scale changes in the sources of Nd by applying a modeling approach. For illustrative purposes we describe rather extreme changes in the magnitude of source fluxes, their isotopic composition or both. We find that the largest effects on Nd result from changes in the boundary source. Considerable changes also result from variations in the magnitude or Nd of dust and rivers but are largely constrained to depths shallower than 1 km, except if they occur in or upstream of regions where deep water masses are formed. From these results we conclude that changes in Nd sources have the potential to affect Nd . However, substantial changes are required to generate large-scale changes in Nd in deep water that are similar in magnitude to those that have been reconstructed from sediment cores or result from changes in meridional overturning circulation in model experiments. Hence, it appears that a shift in Nd comparable to glacial-interglacial variations is difficult to obtain by changes in Nd sources alone, but that more subtle variations can be caused by such changes and must be interpreted with caution.

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“…If ε Nd is treated as a conservative tracer, comparison with non-conservative tracers may also be valuable; for example, its coupling or decoupling with carbon isotope changes through time may provide evidence on productivity, nutrient regeneration or other carbon cycle changes (e.g. Piotrowski et al, 2005;Piotrowski et al, 2008;Piotrowski et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

A boundary exchange influence on deglacial neodymium isotope records from the deep western Indian Ocean

Wilson

Piotrowski

Galy

et al. 2012

Earth and Planetary Science Letters

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Indian Ocean circulation and productivity during the last glacial cycle

Cited by 106 publications

References 77 publications

Mode change of millennial CO ₂ variability during the last glacial cycle associated with a bipolar marine carbon seesaw

Mode change of millennial CO ₂ variability during the last glacial cycle associated with a bipolar marine carbon seesaw

Sensitivity of Nd isotopic composition in seawater to changes in Nd sources and paleoceanographic implications

A boundary exchange influence on deglacial neodymium isotope records from the deep western Indian Ocean

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Indian Ocean circulation and productivity during the last glacial cycle

Cited by 106 publications

References 77 publications

Mode change of millennial CO 2 variability during the last glacial cycle associated with a bipolar marine carbon seesaw

Mode change of millennial CO 2 variability during the last glacial cycle associated with a bipolar marine carbon seesaw

Sensitivity of Nd isotopic composition in seawater to changes in Nd sources and paleoceanographic implications

A boundary exchange influence on deglacial neodymium isotope records from the deep western Indian Ocean

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Mode change of millennial CO ₂ variability during the last glacial cycle associated with a bipolar marine carbon seesaw

Mode change of millennial CO ₂ variability during the last glacial cycle associated with a bipolar marine carbon seesaw